(1) Field of the Invention
The present invention relates to a dielectric barrier discharge lamp that includes external electrodes that are formed at both ends of a glass bulb.
(2) Description of the Related Art
In recent years, as the liquid crystal televisions have become widespread, the demand for the direct-below-type backlight units (hereinafter referred to as LCBL units), which are mounted in the liquid crystal televisions, has increased as well.
Currently, a typical light source of a LCBL unit is a plurality of cold-cathode tube lamps. However, another replacing light source is searched for. One reason for this is that as many high-frequency electronic ballasts as there are cold-cathode tube lamps are required to light the lamps.
When this problem is taken into consideration, the dielectric barrier discharge lamps are suitable for the light source since they require only one high-frequency electronic ballast when they are lighted. For example, 16 number of dielectric barrier discharge lamps may be used suitably as the light source of a LCBL unit.
As shown in FIG. 1, a conventional dielectric barrier discharge lamp 1 is composed of a glass bulb 3 that is a discharge vessel in a shape of a tube, a phosphor 5 that is applied onto an inner surface of the glass bulb 3, mercury 7 that is sealed in the glass bulb 3, a buffer rare gas 9 such as neon and argon, external electrodes 11 and 13 that are conductive resin layers formed on the outer surface of the glass bulb 3 at both ends thereof, and metal conductors 15 and 17 that are in a shape of character C, have spring elasticity, and are connected to resin layers of the external electrodes 11 and 13 (see FIG. 2A) (see Japanese Laid-Open Patent Application No. 2003-17005).
Having studied the conventional dielectric barrier discharge lamp, however, the inventors of the present invention found a problem that the corona discharge may happen during the lamp lighting in which a high voltage as high as 1.0 kV to 3.0 kV is applied to the external electrodes 11 and 13, depending on the positions of the metal conductors 15 and 17 relative to the conductive resin layers of the external electrodes 11 and 13.
FIG. 2A shows the conventional dielectric barrier discharge lamp 1 viewed in the tube axis direction. FIG. 2B is an enlarged side view of the conventional dielectric barrier discharge lamp 1 for explanation of the positions where corona discharges occur.
When, as shown in FIG. 2B, a rim A of the metal conductor 15 in the shape of a character C precedes a rim B of the external electrode 11 toward the center of the glass bulb 3, and when a gap with a distance “h” is generated between the metal conductor 15 and the glass bulb 3, the corona discharge occurs in the gap (this also applies to the side of the metal conductor 17).
When the corona discharge occurs ozone is generated. The generated ozone causes the conductive resin layers, which constitute the external electrode 11, and a resin (not illustrated) that is used in circumference of the lamp to deteriorate rapidly. Even a small amount of ozone may have a disadvantageous effect. That is to say, ozone may decrease the life of the fluorescent lamp, backlight unit, or liquid crystal television by causing the members made of resin to deteriorate.